GPS Speedo Apps - accuracy

[Andy_Pagin]

How accurate are GPS speedos? I've been playing with the Ulysse Speedometer Android app. in my 1967 Landrover it matches the mechanical speedometer exactly (up to 30mph anyway), but in my 1997 Ford Explorer the cars' speedo is always about 5mph faster?
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[Taught2BCauti...]

GPS speedos are generally more accurate than mechanical ones, but some are better than others.

Mechanical speedos in vehicles are designed to read higher than true speed.

Some phones user a lower quality GPS chipset than dedicated GPS devices, and a lot depends on how many satellites are in view, sampling rate, altitude, etc.
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[RhynoCZ]

Very accurate, I've got ''SpeedView'' on xperia-e (android, for free).

The maximum speed that it could ever record was 206 kph, even though the scale is marked up to 240 kph and I was moving way faster than 206 kph. So I'd say 206 kph is the limit for the device I've got.
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[Ariel Badger]

Couple of my mates took them over for their licence qualifying runs at Bonneville Speed week this year but it was rained off
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[angryjonny]

[Kickstart]

Hi

Likely largely depend on the GPS unit itself. Crude system might just calculate speed based on position fixes which might be OK for a slow moving ship. Think the better systems calculate speed based on the doppler effect on the GPS signal. Most will be a basic 1Hz GPS unit, some might be better (the Driftbox performance meter I have uses a 10 Hz GPS unit).

Car speedo can over read by a fair amount (how much varies by vehicle class, but can be up to 10% +8kmh high - and is only checked at a couple of specific speeds), and the accuracy will vary as tyres wear, tyres heat up, different tyres are used, etc.

All the best

Keith
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[RhynoCZ]

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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor